Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $209.26   13.268%   $237.0246   $237.02   $237.00   $237.00  
  Purchase #2 $194.25   6.546%   $206.9656   $206.97   $206.95   $207.00  
  Purchase #3 $204.65   3.498%   $211.8087   $211.81   $211.80   $211.80  
  Purchase #4 $165.91   4.272%   $172.9977   $173.00   $173.00   $173.00  
  Purchase #5 $84.96   10.366%   $93.767   $93.77   $93.75   $93.80  
  Purchase #6 $209.65   5.345%   $220.8558   $220.86   $220.85   $220.90  
  Purchase #7 $227.73   5.713%   $240.7402   $240.74   $240.75   $240.70  
  7 purchase totals = $1,296.41       $1,384.1596   $1,384.17   $1,384.10   $1,384.20